Behavioral and single unit studies are conducted in rabbit, cat, and monkey in experiments on the mechanics and mechanisms of head movements, especially with regard to visually directed gaze transitions. The mechanisms will be examined with chronically implanted electrodes in all neck muscles demonstrated to have a role in head movements. Vectoral planes of force will be identified by stimulation of the muscles directly and by correlation of electromyographic activity with head torque in yaw, pitch, and roll axes following superior collicular stimulation. The mechanisms of central motor control will be examined in single unit studies during active and passive head movements in alert animals. Units will be characterized by 1) whether they have an axon descending to the cervical spinal cord; 2) latency of sensory inputs-vestibular and neck sensory; and 3) association of firing rate with head movement forces in vectoral planes correlating with one or more muscles. The coordinate system regulating motor control of head movements and the role of brainstem structures effecting these movements will be examined for correlates of sensory-motor integration.